That isn't a strong answer, unless the question was about what you think of the code's style. The point is that it's more than just poor style, it's likely to constitute undefined behaviour. Saying different compilers could interpret the expression differently is not equivalent to saying it invokes undefined behaviour.

It's common for interview questions to explore unusual code, perhaps poor quality code, that hinges on edge cases of the language. A candidate with a strong understanding of the language would be expected to take the opportunity to demonstrate it.